Effect of cadmium chloride on secretion of 17β-estradiol by the ovarian follicles of common carp, Cyprinus carpio

Triclosan, an antimicrobial drug, induced reproductive impairment in the freshwater fish, Anabas testudineus (Bloch, 1792)

Triclosan (TCS), an antimicrobial drug, is known to occupy different compartments in aquatic ecosystems. The present study focused to evaluate the reproductive toxicity of triclosan, at environmentally relevant (0.009 and 9 μg L-1) and sublethal (176.7 μg L-1) concentrations for 90 days in the pre-spawning phase of the fish, Anabas testudineus. The reproductive biomarkers, namely, gonadal steroidogenic enzymes, expression of aromatic genes, levels of serum gonadotropins, sex hormones, and histology of gonads were analyzed. The weight of the animal, brain weights along with gonadosomatic index decreased while mucus deposition increased significantly at all concentrations of triclosan as the primary defensive mechanism to prevent the entry of toxicants. Triclosan disrupted gonadal steroidogenesis as evidenced by a reduction in the activities of gonadal steroidogenic enzymes. The expressions of cyp19a1a and cyp19a1b genes were up-regulated in the brain of both sexes and testis, while down-regulated in the ovary indicating estrogenic effects of the compound. The endocrine-disrupting effects of triclosan were confirmed. The current results suggest that chronic exposure to triclosan altered reproductive endpoints thereby impairing normal reproductive functions in fish.

Cadmium as an ovarian toxicant: A review

Cadmium (Cd) is a ubiquitous heavy metal toxicant with no biological function in the human body. Considerably, because of its long biological half-life and very low excretion rate, Cd is inclined to accumulate and cause deleterious effects on various body organs (e.g., liver, kidney, and ovary) in humans and animals. Ovaries are the most vulnerable targets of Cd toxicity. Cd has been shown to induce oxidative stress, follicular atresia, hormonal imbalance, and impairment of oocyte growth and development. Moreover, Cd toxicity has been associated with increasing incidences of menstrual disorders, pregnancy loss, preterm births, delayed puberty, and female infertility. Therefore, it is crucial to understand how Cd poisoning impacts specific ovarian processes for the development of preventive interventions to enhance female fertility. The current review attempts to collate the recent findings on Cd-induced oxidative stress, follicular apoptosis, steroid synthesis inhibition, and teratogenic toxicity, along with their possible mechanisms in the ovarian tissue of different animal species. Additionally, the review also summarizes the studies related to the use of many antioxidants, medicinal herbs, and other compounds as remedial approaches for managing Cd-induced ovarian toxicity.

Cumulus Cell Transcriptome after Cumulus-Oocyte Complex Exposure to Nanomolar Cadmium in an In Vitro Animal Model of Prepubertal and Adult Age

Cadmium (Cd), a highly toxic pollutant, impairs oocyte fertilization, through oxidative damage on cumulus cells (CCs). This study analysed the transcriptomic profile of CCs of cumulus-oocyte complexes (COCs) from adult and prepubertal sheep, exposed to Cd nanomolar concentration during in vitro maturation. In both age-groups, CCs of matured oocytes underwent RNA-seq, data analysis and validation. Differentially expressed genes (DEGs) were identified in adult (n = 99 DEGs) and prepubertal (n = 18 DEGs) CCs upon Cd exposure. Transcriptomes of adult CCs clustered separately between Cd-exposed and control samples, whereas prepubertal ones did not as observed by Principal Component Analysis. The transcriptomic signature of Cd-induced CC toxicity was identified by gene annotation and literature search. Genes associated with previous studies on ovarian functions and/or Cd effects were confirmed and new genes were identified, thus implementing the knowledge on their involvement in such processes. Enrichment and validation analysis showed that, in adult CCs, Cd acted as endocrine disruptor on DEGs involved in hormone biosynthesis, cumulus expansion, regulation of cell signalling, growth and differentiation and oocyte maturation, whereas in prepubertal CCs, Cd affected DEGs involved in CC development and viability and CC-oocyte communications. In conclusion, these DEGs could be used as valuable non-invasive biomarkers for oocyte competence.

Synthesis, Regulatory Factors, and Signaling Pathways of Estrogen in the Ovary

New insights have been thrown for understanding the significant role of estrogen on various systems of humans. Increasing evidences have determined the significant roles of estrogen in female reproductive system. So, the normal synthesis and secretion of estrogen play important roles in maintaining the function of tissues and organs. The ovaries are the main synthetic organs of estrogen. In this review, we summarized the current knowledge of the estrogen synthesis in the ovaries. A series of factors and signaling pathways that regulate the synthesis of estrogen are expounded in detail. Understanding the regulating factors and potential mechanism related to estrogen synthesis will be beneficial for understanding estrogen disorder related diseases and may provide novel therapeutic targets.

cAMP signaling in ovarian physiology in teleosts: A review

Ovarian function in teleosts, like in other vertebrates, is regulated by two distinct gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin effects are mediated by membrane-bound G protein-coupled receptors localized on the surface of follicle cells. Gonadotropin receptor activation results in increased intracellular cAMP, the most important second cellular signaling molecule. FSH stimulation induces the production of 17β-estradiol in the cells of growing follicles to promote vitellogenesis in oocytes. In contrast, in response to LH, fully grown post-vitellogenic follicles gain the ability to synthesize maturation-inducing steroids, which induce meiotic resumption and ovulation. All these events were induced downstream of cAMP. In this review, we summarize studies addressing the role of the cAMP pathway in gonadotropin-induced processes in teleost ovarian follicles. Furthermore, we discuss future problems concerning cAMP signaling in relation to teleost ovarian function and the differences and similarities in the gonadotropin-induced cAMP signaling pathways between mammals and teleosts.

Environmental cadmium exposure during gestation impairs fetal brain and cognitive function of adult offspring via reducing placenta-derived E2 level

Early-life exposure to environmental cadmium (Cd) is known to cause developmental disorders, yet the effect and mechanism of gestational exposure to Cd on the offspring's cognitive function remains unclear. Placenta as a well-established target organ for Cd-impaired fetal development, its role in estrogen regulation and offspring cognitive function is unknown. Our in vivo experiments found that gestational Cd exposure impaired cognitive function in adult male offspring, accompanied with lowered 17β-estradiol (E2) level in the male fetal brain upon Cd exposure. Correspondingly, the expression of synapse-associated proteins including brain-derived neurotrophic factor (BDNF), post-synaptic density protein 95 (PSD95) and synapsin-1 were downregulated, which were reversed when supplemented with E2 hormone during gestation. Further observation showed placental estrogen synthesis inhibition and general control non-derepressible 2 (GCN2) signaling activation upon Cd exposure, whereas placental estrogen synthesis could be restored through inhibiting GCN2 activity. Based on ovariectomy (OVX) of pregnant mice, we confirmed that Cd exposure reduced E2 level in fetal brain via inhibiting placenta-derived estrogen synthesis. The aforementioned Cd-induced fetal brain injury and cognitive impairment in adult offspring were significantly alleviated when pregnant dams were supplemented with anti-stress agent N-Acetyl-l-cysteine. In summary, Cd disrupted placenta-derived estrogen synthesis via activating GCN2 signaling, and thereby caused cognitive impairment in adult offspring mice. Our findings suggest that placenta-derived estrogen may be an effect marker of environmental toxicants-evoked cognitive dysfunction in adult offspring and suggest that environmental toxicants may affect the fetal brain development via placenta-fetal-brain axis.

Effect of combined exposure to silica nanoparticles and cadmium chloride on female zebrafish ovaries

Silica nanoparticles (SiNPs) and cadmium chloride (CdCl2) are two important environmental pollutants. In previous research, found that SiNPs in zebrafish larvae can amplify the cardiovascular damage caused by cadmium. Whether SiNPs in the ovaries can amplify the adverse effects of cadmium on the zebrafish ovaries is worth studying problem. In this study, sexually mature female zebrafish were used as model organisms and exposed to 1 μmol/L CdCl2 and/or 25 μg/mL SiNPs for 30 days. The results showed that the structure and function of ovaries in the sole and combined exposure groups changed significantly, resulting in reduced ovarian quality, decreased number of mature oocytes, and the development of malformed offspring. A deep-sequencing analysis showed that organisms' lipid metabolism and transportation, estrogen metabolism, and response to the maturation, meiosis, and vitellogenin synthesis of oocytes were significantly affected by single exposure or combined exposure. These findings provide further insights into the harm of cooperation of CdCl2 and/or SiNPs to the aquatic ecosystems.

Chronic exposure to environmental cadmium affects growth and survival, cellular stress, and glucose metabolism in juvenile channel catfish (Ictalurus punctatus)

Anthropogenic activities have led to the enrichment of cadmium in freshwater systems where it is a contaminant of concern for fisheries and aquaculture as it has no known biological function and is toxic at trace concentrations. Yet, knowledge gaps remain regarding effects of chronic exposure to environmentally relevant concentrations on freshwater fish. Thus, the objectives of the current study were to assess chronic impacts of cadmium on channel catfish (Ictalurus punctatus) including how tissue-specific bioaccumulation patterns relate to functions of those tissues over time. We focused on liver and kidneys, and expression of genes related to cellular stress, glucose metabolism, and steroidogenesis. Catfish were exposed to concentrations of 0.5 (control), 2 (low), and 6 (high) μg L^-1 Cd from fertilization to six months. Cadmium exposure negatively impacted channel catfish growth and was linked to bioaccumulation of tissue Cd, which followed a dose-related response, where concentrations in trunk kidney > liver = head kidney >> muscle. Differences in tissue Ca, Cu, Fe, and Zn concentrations were also observed between treatments. Following 3 months of exposure, expression of metallothionein (MT) and heat shock proteins (HSP) 70 & 90 increased relative to controls; however, no differences were detected at 6 months, suggesting compensation. Conversely, there were no differences in expression patterns for key genes in steroidogenesis, steroidogenic factor 1 (SF1), steroidogenic acute regulatory protein (StAR), and cytochrome P450scc (P450), which supports the observation that Cd did not affect the secondary stress response, evaluated via plasma cortisol and glucose concentrations following a low water stress event. As a function of length and weight, the high Cd treatment yielded fish that were significantly smaller than controls. In addition to the cellular responses in MT and HSPs noted, reduced growth in the high Cd treatment was likely due, at least in part, to elevated energetic demands. This is supported by observations of the upregulation of genes necessary for glucose metabolism. Hexokinase (HK), glucose-6-phosphatase (G6P), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were significantly elevated in the high treatment relative to controls at 3 months of exposure. Over the study period, exposure also reduced survival of channel catfish from 3 to 6 months. Reduced fitness, as a consequence of cadmium exposure, could be visible at the population level through altered life histories and growth patterns.

Blood metal levels and serum testosterone concentrations in male and female children and adolescents: NHANES 2011-2012

Environmental exposure to metals is ubiquitous, but its relation to androgen hormone levels is not well understood, especially in children and adolescents. This study aimed to explore the relationship between blood metal concentrations (lead, cadmium, total mercury, selenium, and manganese) and serum total testosterone (TT) levels in 6–19-year-old children and adolescents in the National Health and Nutrition Examination Survey (NHANES) 2011–2012. Weighted multivariable linear regression models using NHANES sampling weights were employed to evaluate the association between log-transformed serum TT and each metal categories in male and female children (age 6-11years) and adolescents (age 12–19 years). We established that blood cadmium and manganese levels were associated with significantly higher serum TT levels in the female adolescents. Additionally, the blood selenium levels in male adolescents were related to significantly higher serum TT. No significant associations between blood lead or total mercury levels and TT were observed in children or adolescents of either sex. These findings suggest that environmental exposure to certain metals could affect serum TT levels in adolescents, which might have important implications for the health of adolescents. Further research is required to confirm and extend our present findings.

Exposure to environmentally relevant cadmium concentrations negatively impacts early life stages of channel catfish (Ictalurus punctatus)

Cadmium is a persistent contaminant of surface waters. The effects of cadmium on early life stages of fish are not well understood, although they are often disproportionately affected by contaminants. The objectives of this study were to examine effects of chronic exposure to environmentally relevant concentrations on growth, development, cellular stress, and glucose metabolism of channel catfish, Ictalurus punctatus. Eggs were wet-fertilized in treatment water at concentrations of 0.4 (control), 2.2 (low), or 8.5 (high) μg L^-1 and monitored through swim-up, black fry stage. Eggs and fry accumulated cadmium dose-dependently. Fertilization rates were unaffected, yet hatch rate was significantly reduced in the high treatment. Survival to black fry and overall size and condition factor were not affected; however, differences in yolk sac size, and presumably energetics of yolk fry, was detected. Physiological pathways were also affected, demonstrated by altered gene expression, most notably in genes related to carbohydrate metabolism. Elevated expression of HK and G6PD, rather than G6P and GADPH, suggests glucose may be shunted towards the pentose-phosphate pathway. Overall, observations indicate cadmium negatively affects development in early life stages of channel catfish, which could lead to shifts in population structure and life history patterns in exposed populations of wild fish.

Joint effects of chronic exposure to environmentally relevant levels of nonylphenol and cadmium on the reproductive functions in male rockfish Sebastiscus marmoratus

Nonylphenol (NP) and Cadmium (Cd) are two common contaminants that can be detected in aquatic environments. Nevertheless, the combined toxicity of NP and Cd at environmentally relevant concentrations in aquatic organisms has not been thoroughly characterized to date. In the present study, the interactions between NP and Cd on male Sebastiscus marmoratus were studied. After 21 days of exposure, the brain aromatase activity was observed to be significantly induced by 100 ng/L NP and 40 μg/L Cd, whereas all of the concentrations of co-treatment resulted in an increase in brain aromatase activity. Additionally, NP could also reduce plasma testosterone concentration, while NP, Cd and their mixture could induce plasma 17β-estradiol (E2) concentration and VTG concentration. The interactions between NP and Cd on the reproductive physiology were antagonism. Our results also support the notion of using these indicators as biomarkers for exposure to EDCs and further extend the boundary of biomonitoring to environmental levels.

Seasonal ovarian development in relation to the gonadotropins, steroids, aromatase and steroidogenic factor 1 (SF-1) in the banded gourami, Trichogaster fasciata

The endocrine regulation of gonadal development and annual variation of key sex steroids is the basic knowledge to understand the reproductive cycle of teleost fish. Present study was aimed to investigate the levels of gonadotropins in relation to the follicular development and plasma steroids during the reproductive cycle of female Trichogaster fasciata. Female fish were sampled and ovarian development is described histologically throughout the year in relation to the seasonal variations of gonadosomatic index (GSI); follicle stimulating hormone (FSH) and luteinizing hormone (LH); three key steroids for folliculogenesis and maturation i.e. testosterone (T), 17β-estradiol (E₂) and 17α20βdihydroxy4pregnen3one (17,20β-P). Relatively higher level of FSH was observed till the ovary reaches in late vitellogenic stage confirms that FSH regulates the early folliculogenesis of the ovary, whereas LH peak was observed in the postvitellogenic stage, which indicates that maturation and ovulation were controlled by LH. Seasonal steroid profiles show that both T and E₂ reach its maximum level prior to the 17,20β-P which attain its peak value in the month of August. Thus, single peak values of LH and 17,20β-P coinciding with GSI peak, clearly indicates that T. fasciata breeds only once in a year. Furthermore, to elucidate the molecular basis of the reproductive cycle, this study analyzes the other key factors of ovarian function such as cyp19a1a gene expression, aromatase activity and SF-1 localization throughout the year. cyp19a1a gene expression and the aromatase activity were highest in vitellogenic stages indicate that relatively higher E₂ production in this stage is regulated by FSH. Immunohistochemical localizations of aromatase and SF-1 in the cellular layer of oocytes demonstrated that aromatase is FSH-dependent and SF-1 could be regulated by both FSH and LH as relatively higher amount of aromatase was localized in the vitellogenic stage oocytes than the postvitellogenic and post germinal vesicle breakdown (post-GVBD) stages; whereas, high amount of SF-1 was observed in vitellogenic, postvitellogenic and post-GVBD stages. These data regarding the reproductive endocrinology of T. fasciata may be useful to understand the interaction between gonadotropins, steroids, aromatase and SF-1 in teleost fishes and may contribute to restoration of the ecologically important fish through artificial reproduction.

Effects of calcium and estrogen on the development of the ceratohyal cartilage in zebrafish (Danio rerio) larvae upon embryo and maternal cadmium exposure

The present study is to investigate the reason why the ceratohyal cartilage (CH) angle of zebrafish larvae were larger compared to the control group after their female parents were treated with cadmium (F-Cd). However, the CH angle was smaller compared to the control group when embryos were directly exposed to Cd²⁺ for 72 h (D-Cd). Results showed that calcium contents of larvae were lower than the control, but the transporter isoforms trpv4 and trpv6 mRNA expressions were significantly increased upon D-Cd treatment. Furthermore, external Ca²⁺ added during D-Cd treatment reveals that the CH angles of larvae did not appear significantly different compared to the control. On the other hand, E2 (17β-estradiol) contents were higher around 1.9 folds in the ovaries of females; CH angle were over 25°, and Cd²⁺ contents were higher around 6 folds than the control group on larvae treated through F-Cd treatment; CH angles and E2 levels on larvae were higher than the control after the larvae were treated with 1.84 μM E2 (D-E2); Estradiol receptor (ER) isoforms ERβ1 and ERα mRNA expressions significantly increased when 0 hpf embryos were either treated with D-E2 or D-Cd. According to the results, we suggested that the CH angle of larvae become larger upon F-Cd treatment due to maternal Cd²⁺ inducing E2 levels. However, the CH angle of larvae appeared to be smaller compared to the control upon D-Cd treatment. We suggested that the CH angle decreased due to the decrease of Ca²⁺ contents upon Cd²⁺ exposure.

Effects of bisphenol A (BPA) on brain-specific expression of cyp19a1b gene in swim-up fry of Labeo rohita

Estrogen regulates numerous developmental and physiological processes and effects are mediated mainly by estrogenic receptors (ERs), which function as ligand-regulated transcription factor. ERs can be activated by many different types endocrine disrupting chemicals (EDCs) and interfere with behaviour and reproductive potential of living organism. Estrogenic regulation of membrane associated G protein-coupled estrogen receptor, GPER activity has also been reported. Bisphenol A (BPA), a ubiquitous endocrine disruptor is present in many household products, has been linked to many adverse effect on sexual development and reproductive potential of wild life species. The present work is aimed to elucidate how an environmentally pervasive chemical BPA affects in vivo expression of a known estrogen target gene, cyp19a1b in the brain, and a known estrogenic biomarker, vitellogenin (Vg) in the whole body homogenate of 30 days post fertilization (dpf) swim-up fry of Labeo rohita. We confirm that, like estrogen, the xenoestrogen BPA exposure for 5-15 days induces strong overexpression of cyp19a1b, but not cyp19a1a mRNA in the brain and increase concentration of vitellogenin in swim-up fry. BPA also induces strong overexpression of aromatase B protein and aromatase activity in brain. Experiments using selective modulators of classical ERs and GPER argue that this induction is largely through nuclear ERs, not through GPER. Thus, BPA has the potential to elevate the levels of aromatase and thereby, levels of endogenous estrogen in developing brain. These results indicate that L. rohita swim-up fry can be used to detect environmental endocrine disruptors either using cyp19a1b gene expression or vitellogenin induction.

Protective effect of melatonin on cadmium-induced changes in some maturation and reproductive parameters of female Prussian carp (Carassius gibelio B.)

The aim of this study was to determine whether melatonin (Mel), which is a known antioxidant and free radical scavenger, could perform the role of a preventive agent against the toxic effects of cadmium (Cd²⁺) on mortality, fish growth, gonadosomatic index (GSI), luteinizing hormone (LH) secretion, the response to hormonal stimulation of spawning, and also tissue accumulation of Cd in Prussian carp females. These females received melatonin implants and were exposed to 0.4 or 4.0 mg/L of Cd (as CdCl₂·2.5H₂O) over either a 5- or 3-month period, followed by further 2 months of purification in clear water. Negative changes caused by exposure to cadmium in the water were as follows: higher fish mortality, lower body weight, increased accumulation of cadmium in the brain and ovary, lowered GSI, impaired spontaneous LH secretion during exposure, and impaired LH secretion during stimulation of spawning. All of these effects were observed in the group of fish exposed to 0.4 and/or 4.0 mg Cd/L but did not occur or were less pronounced in the groups exposed to cadmium in the presence of melatonin released from the implants. During depuration, in the group of fish which had been exposed to the highest Cd concentration, we observed a significant improvement in fish survival rate, body growth, inhibition of further cadmium accumulation in tissues, and gradual return of spontaneous LH secretion as well as normalization of the GSI value to the control group levels. In conclusion, these findings indicate that melatonin can be a preventive agent for some toxic effects on fish reproduction induced by environmental cadmium contamination.

Environmental doses of perfluorooctanoic acid change the expression of genes in target tissues of common carp

We aimed to evaluate the effects of environmental doses of perfluorooctanoic acid (PFOA) on bioconcentration and gene expression in common carp (Cyprinus carpio). Adult male and female carp were exposed to environmental (200 ng/L) and experimental (2 mg/L) doses of PFOA for 56 d. Carp exposed to 200 ng/L had levels of PFOA below the level of detection in all tissue samples analyzed, whereas variable concentrations were measurable in various tissues from carp exposed to 2 mg/L. The expression level of the glutathione S-transferase (GST) gene, coding for a detoxifying enzyme, increased in a PFOA dose-dependent manner in liver tissues from 200 ng/L to 2 mg/L exposure (p < 0.05). The expression levels of CYP19A gene, coding for the enzyme that converts testosterone into estrogen, were altered in gonadal tissues from male and female carp exposed to either 200 ng/L or 2 mg/L; expression increased in male gonads and decreased in female gonads. Unexpectedly, the expression levels of CYP19A in male and female gonads from carp exposed to 200 ng/L or 2 mg/L were similar (p > 0.05). Therefore, even though environmental doses of PFOA did not accumulate in tissues of the common carp, they did affect the gene expression levels of GST in the liver and CYP19A in the gonads. These observations raise concerns that exposure to environmental doses of PFOA may affect gene expression in animals and possibly in humans, with important health consequences. Environ Toxicol Chem 2018;37:942-948. © 2017 SETAC.

Estrogen-regulated expression of P450arom genes in the brain and ovaries of adult female Indian climbing perch, Anabas testudineus

Cytochrome P450arom (CYP19), a product of cyp19a1 gene, catalyzes the conversion of androgens to estrogens and is essential for regulation of reproductive function in vertebrates. In the present study, we isolated partial cDNA encoding the ovarian (cyp19a1a) and brain (cyp19a1b) P450arom genes from adult female perch, Anabas testudineus and investigated their regulation by estrogen in vivo. Results demonstrated that cyp19a1a and cyp19a1b predominate in ovary and brain respectively, with quantity of both attuned to reproductive cycle. To elucidate estrogen-regulated expression of cyp19a1b in brain and cyp19a1a in ovary, dose- and time-dependent studies were conducted with estrogen in vitellogenic-stage fish in the presence or absence of specific aromatase inhibitor fadrozole. Results demonstrated that treatment of fish with 17β-estradiol (E2; 1.0 μM)) for 6 days caused significant upregulation of cyp19a1b transcripts, aromatase B protein, and aromatase activity in brain in a dose- and time-dependent manner. Ovarian cyp19a1a mRNA, aromatase protein, and aromatase activity, however, was less responsive to E2 than brain. Treatment of fish with an aromatase inhibitor fadrozole for 6 days attenuated both brain and ovarian cyp19a1 mRNAs expression and stimulatory effects of E2 was also significantly reduced. These results indicate that expression of cyp19a1b in brain and cyp19a1a in ovary of adult female A. testudineus was closely associated to plasma E2 levels and seasonal reproductive cycle. Results further show apparent differential regulation of cyp19a1a and cyp19a1b expression by E2/fadrozole manipulation.

Molecular mechanism of mercury-induced reproductive impairments in banded gourami, Trichogaster fasciata

Mercury is one of the key pollutants responsible for the degradation of natural aquatic ecosystems. Among the different forms of mercury that exist in the environment, mercuric chloride (HgCl₂) is the dominant pollutant for freshwater environments as it is used as an ingredient in antiseptics, disinfectants and preservatives, insecticides, batteries and in metallurgical and photographic operations. Pollutant may exert their action on organisms or populations by affecting their normal endocrine function as well as reproduction. Thus, the present study tried to understand the effect of mercuric chloride (HgCl₂) on reproductive function and to decipher the molecular mechanism of Hg-induced reproductive impairments of female Trichogaster fasciata. Both in vivo and in vitro experiments were performed by using ecologically relevant doses of HgCl₂ and the resulting effects on follicular development, steroidogenic potentiality, aromatase activity, aromatase gene expression and steroidogenic factor-1 (SF-1) expression pattern were analysed. In vivo exposure to HgCl₂ caused reproductive impairments as shown by the inhibitory role of HgCl₂ on follicular development, steroid biosynthesis and SF-1 activity. In vitro experiments revealed that aromatase activity, steroidogenesis, aromatase and SF-1 expression were blocked by HgCl₂. The results obtained from this study contribute to understand the molecular mechanism of HgCl₂-induced reproductive impairment of T. fasciata.

Estrogen-regulated expression of cyp19a1a and cyp19a1b genes in swim-up fry of Labeo rohita

P450 aromatase is the terminal enzyme in the steroidogenic pathway and catalyzes the conversion of androgens to estrogens. The expression of cyp19a1 genes in brain and gonad of Indian major carp, Labeo rohita swim-up fry was measured by quantitative real-time polymerase chain-reaction. Results demonstrated that cyp19a1b and cyp19a1a predominate in brain and gonad respectively. Treatment of fry with an aromatase inhibitor fadrozole for 6days attenuated brain cyp19a1b expression, but not cyp19a1a of gonad. Fadrozole also attenuated brain aromatase activity. Treatment with 17β-estradiol (E2) for 6days resulted in up-regulation of brain cyp19a1b transcripts in a dose- and time-dependent manner, but not cyp19a1a. Whole-body concentration of vitellogenin also increased in response to E2. Altogether, these results indicate L. rohita swim-up fry can be used to detect environmental estrogens either using vitellogenin induction or cyp19a1b gene expression.

Exposure to cadmium during in vitro maturation at environmental nanomolar levels impairs oocyte fertilization through oxidative damage: A large animal model study

Cadmium is a highly toxic heavy metal with negative effects on oocyte fertilization. The aim of this study was to analyse whether cadmium-induced impairment of fertilization is caused by mitochondria dysfunction and oxidative stress in the cumulus-oocyte complex (COC). Preliminarily, 19 trace element levels were measured in ovaries from juvenile and adult ewes and age-related cadmium ovarian bioaccumulation at nanomolar concentrations was found. COCs from juvenile and adult ewes, exposed during in vitro maturation to 1nM or 100nM CdCl₂, and subjected to in vitro fertilization showed significantly lower fertilization rates in exposed COCs compared with controls. In vitro matured exposed and control COCs underwent confocal microscopy analysis of mitochondria activity and reactive oxygen species (ROS) levels and lipid peroxidation (LPO) assay at cumulus cell and oocyte level. In both age groups, cadmium at nanomolar concentrations induced cumulus-oocyte mitochondria over-activity and oxidative damage which were related to impaired oocyte fertilization.

Membrane receptor cross talk in gonadotropin-, IGF-I-, and insulin-mediated steroidogenesis in fish ovary: An overview

Gonadal steroidogenesis is critical for survival and reproduction of all animals. The pathways that regulate gonadal steroidogenesis are therefore conserved among animals from the steroidogenic enzymes to the intracellular signaling molecules and G protein-coupled receptors (GPCRs) that mediate the activity of these enzymes. Regulation of fish ovarian steroidogenesis in vitro by gonadotropin (GtH) and GPCRs revealed interaction between adenylate cyclase and calcium/calmodulin-dependent protein kinases (CaMKs) and also MAP kinase pathway. Recent studies revealed another important pathway in GtH-induced fish ovarian steroidogenesis: cross talk between GPCRs and membrane receptor tyrosine kinases. Gonadotropin binding to Gαs-coupled membrane receptor in fish ovary leads to production of cAMP which in turn trans-activate the membrane-bound epidermal growth factor receptor (EGFR). This is followed by activation of ERK1/2 signaling that promotes steroid production. Interestingly, GtH-induced trans-activation of EGFR in the fish ovary uniquely requires matrix-metalloproteinase-mediated release of EGF. Inhibition of these proteases blocks GtH-induced steroidogenesis. Increased cAMP production in fish ovarian follicle upregulate follicular cyp19a1a mRNA expression and aromatase activity leading to increased biosynthesis of 17β-estradiol (E2). Evidence for involvement of SF-1 protein in inducing cyp19a1a mRNA and aromatase activity has also been demonstrated. In addition to GtH, insulin-like growth factor (IGF-I) and bovine insulin can alone induced steroidogenesis in fish ovary. In intact follicles and isolated theca cells, IGF-I and insulin had no effect on GtH-induced testosterone and 17a,hydroxysprogeaterone production. GtH-stimulated E2 and 17,20bdihydroxy-4-pregnane 3-one production in granulosa cells however, was significantly increased by IGF-I and insulin. Both IGF-I and insulin mediates their signaling via receptor tyrosine kinases leading to activation of PI3 kinase/Akt and MAP kinase. These kinase signals then activates steroidogenic enzymes which promotes steroid production. PI3 kinase, therefore considered to be an initial component of the signal transduction pathways which precedes MAP kinase in IGF-1 and insulininduced steroidogenesis in fish ovary. Thus, investigation on the mechanism of signal transduction regulating fish ovarian steroidogenesis have shown that multiple, apparently independent signal transduction pathways are needed to convey the message of single hormone or growth factor.

Associations of urinary cadmium with circulating sex hormone levels in pre- and postmenopausal Japanese women

BACKGROUND

Exposure to cadmium has been suspected as a risk factor for breast cancer. The present study examined the associations between urinary cadmium levels and circulating sex hormone levels that are linked to breast cancer risk in healthy women.

METHODS

The study subjects were 396 premenopausal Japanese women who had regular menstrual cycles less than 40 days long and 207 postmenopausal Japanese women. Urinary cadmium was measured using spot urine samples. Plasma estradiol, testosterone, and dehydroepiandrosterone sulfate were measured. Additionally, the follicle-stimulating hormone, luteinizing hormone, and sex hormone-binding globulin were measured for premenopausal women.

RESULTS

In premenopausal women, the urinary cadmium level either expressed in μg per liter or per g of urine creatinine was significantly inversely associated with total and free testosterone levels after controlling for age, body mass index, smoking status, alcohol intake, and the phase of the menstrual cycle. Total and free testosterone levels were 14.6% and 15.0% lower, respectively, in women in the highest quartile of urinary cadmium per g creatinine in those in the lowest quartile. In postmenopausal women, the urinary cadmium in μg per liter as well as per g creatinine was significantly inversely associated with the estradiol level after controlling for covariates. The estradiol level was 25.8% lower in women in the highest tertile of urinary cadmium per g creatinine than in those in the lowest tertile.

CONCLUSIONS

The data suggest inverse associations between urinary cadmium and the plasma estradiol or testosterone level in Japanese women.

GnIH plays a negative role in regulating GtH expression in the common carp, Cyprinus carpio L

In birds and mammals, the gonadotrophin-inhibitory hormone (GnIH) effectively inhibits the expression of gonadotrophin (GtH). In teleosts, the effects of GnIH are still unclear and under much debate. The aim of this study is to evaluate the functions of GnIH/receptors of gonadotrophin-inhibitory hormone (GnIHRs) system during reproduction in the common carp, Cyprinus carpio L. We cloned the full cDNA sequences of GnIH /GnIHRs. Real-time PCR results showed that GnIH/GnIHRs were distributed extensively across the whole hypothalamus-pituitary-gonad (HPG) axis. We also examined the changes of GnIH/GnIHRs in the HPG axis during reproduction. GnIH mRNA expression was decreased to the minimum value in Apr, the spawning month, and increased immediately after the completion of reproduction. Expression pattern of GnIH during reproduction was the opposite to those of Gonadotrophin release hormone 3 (GnRH3) and luteinizing hormone (LH). Expression patterns of GnIHRs were similar to that of GnIH in the hypothalamus. In the pituitary, GnIHR2/3 peaked in March before spawning. In the ovaries, the GnIHR1 decreased to the minimum value in April, but GnIHR2/3 increased. By injection and incubation with synthesized GnIH-III peptide, we confirmed the negative influence of GnIH on mRNAs of the follicle-stimulating hormone-β and LH-β subunits in the common carp. These results show that the GnIH/GnIHRs system is involved in the negative regulation of reproduction in HPG axis of the common carp.

Gonadotropin and sf-1 regulation of cyp19a1a gene and aromatase activity during oocyte development in the rohu, L. rohita

Cytochrome P450 aromatase (P450arom), a product of cyp19a1 gene, plays pivotal roles in vertebrate steroidogenesis and reproduction. In this study, we isolated partial cDNA encoding the ovarian (cyp19a1a) and brain (cyp19a1b) P450arom genes from adult female rohu, Labeo rohita and investigated the regulation of cyp19a1a by gonadotropin and SF-1. The cyp19a1a and cyp19a1b were expressed predominantly in the ovary and brain respectively, with quantity of the former attuned to reproductive cycle. To elucidate gonadotropin regulation of cyp19a1a mRNA expression and P450 aromatase activity for 17β-estradiol (E2) biosynthesis in vitro by the vitellogenic ovarian follicles, time- and dose-dependent studies were conducted with HCG and porcine FSH. Results demonstrated that HCG stimulated significantly higher expression of cyp19a1a mRNA and aromatase activity leading to increased biosynthesis of E2 than FSH. To understand the involvement of SF-1 to in the regulation of cyp19a1a and aromatase activity, ovarian follicles were incubated with increasing concentrations of HCG and expression of sf1gene and activation of SF-1 protein were measured. Results demonstrated that HCG significantly induced expression of sf-1 gene and activation of SF-1 protein suggesting a link between SF-1 and P450 aromatase activation in this fish ovary during gonadotropin-induced steroidogenesis.

Effects of phenol on ovarian P450arom gene expression and aromatase activity in vivo and antioxidant metabolism in common carp Cyprinus carpio

Ovarian cyp19a mRNA expression and P450 aromatase activity were measured in vivo in common carp Cyprinus carpio exposed to phenol for 96 h. Production of reactive oxygen species (ROS) and parameters of antioxidant defense system in serum ovary and liver of this fish after long-term phenol exposure were also studied. In vivo exposure of fish to sublethal dose of phenol for 96 h caused marked attenuation of ovarian cyp19a1a gene expression and P450 aromatase activity. Production of ROS like hydrogen peroxide and hydroxyl radicals in serum, liver and ovary in fish exposed to phenol for 15 days elevated significantly from day 1 to day 7 with no further significant increase thereafter compared to their respective control values. Total superoxide dismutase (SOD) and catalase activities in serum and ovary decreased gradually and significantly from day 1 to day 4, which then increased significantly for the rest of the exposure days. Liver SOD activity seemed to be distinctly responsive to phenol. SOD activity in liver of phenol-exposed fish started to increase gradually from day 1 to 4 with no further increase thereafter. Catalase activities in all the tissues showed significant inhibition up to day 4 which then increased gradually and significantly up to day 15 of phenol exposure compared to their respective control values. From our results, it appears that sublethal dose of phenol has the endocrine disruptive potential and effect is mediated via inhibition of ovarian P450arom gene expression and aromatase activity in vivo. Sublethal dose of phenol also caused oxidative stress, and antioxidant systems are very much effective to prevent the damages caused by the generation of ROS.

Subchronic effects of cadmium on the gonads, expressions of steroid hormones and sex-related genes in tilapia Oreochromis niloticus

Cadmium (Cd) is one of the most toxic heavy metals in aquatic ecosystem which affects fish health and aquaculture. In the present study, we examined the bioaccumulation of Cd in the gonads of tilapia via dissolved and dietary routes. We evaluated the subchronic effects of Cd on the histology of gonads, steroid hormone levels and sex-related gene expressions in tilapia. In addition, we also studied maternal transfer of Cd. Our results indicated that Cd was accumulated significantly in both ovary and testis from both exposure routes. Histopathological analysis showed that Cd induced ovary and testis injuries. Estradiol levels were significantly increased in dissolved Cd exposed female fish. In addition, the Cd exposure displayed different effects on gene expressions in gonads. In females, the estrogen receptor (ERα) was stimulated in dissolved Cd-exposed fish at 70.32 and 143.78 μg/L for 30 days and in fish at 143.78 μg/L for 60 days. Vitellogenin expression was significantly down-regulated in the ovary of dissolved Cd-exposed fish. In testis, GR expression was elevated after 60 days of dissolved Cd and dietary exposure. Furthermore, Cd level was significantly higher in the eggs than that in the fry. Our results demonstrated that both dissolved and dietary Cd exposures affected gonad development by altering steroid hormone levels and sex-related gene expressions in tilapia.

Associations between cadmium exposure and circulating levels of sex hormones in postmenopausal women

Recent epidemiological as well as in vivo and in vitro studies collectively suggest that the metalloestrogen cadmium (Cd) could be a potential risk factor for hormone-related cancers in particularly breast cancer. Assessment of the association between Cd exposure and levels of endogenous sex hormones is of pivotal importance, as increased levels of such have been associated with a higher risk of breast cancer in postmenopausal women. The present study investigated the perceived relationship (multivariable-adjusted linear regression analyses) between Cd exposure [blood Cd (B-Cd) and urinary Cd (U-Cd)], and serum levels of androstenedione, testosterone, estradiol, and sex-hormone binding globulin (SHBG), in 438 postmenopausal Swedish women without hormone replacement therapy (HRT). A significant positive association between B-Cd (median 3.4 nmol/L) and serum testosterone levels, as well as a significant inverse association between B-Cd and serum estradiol levels and with the estradiol/testosterone ratio were encountered. However, U-Cd (median 0.69 nmol/mmol creatinine) was inversely associated with serum estradiol levels only. Our data may suggest that Cd interferes with the levels of testosterone and estradiol in postmenopausal women, which might have implications for breast cancer risk.

Metal-PAH mixtures in the aquatic environment: a review of co-toxic mechanisms leading to more-than-additive outcomes

Mixtures of metals and polycyclic aromatic hydrocarbons (PAHs) occur ubiquitously in aquatic environments, yet relatively little is known regarding their combined toxicities. Emerging reports investigating the additive mortality in metal-PAH mixtures have indicated that more-than-additive effects are equally as common as strictly-additive effects, raising concern for ecological risk assessment typically based on the summation of individual toxicities. Moreover, the current separation of focus between in vivo and in vitro studies, and fine- and coarse-scale endpoints, creates uncertainty regarding the mechanisms of co-toxicity involved in more-than-additive effects on whole organisms. Drawing from literature on metal and PAH toxicity in bacteria, protozoa, invertebrates, fish, and mammalian models, this review outlines several key mechanistic interactions likely to promote more-than-additive toxicity in metal-PAH mixtures. Namely, the deleterious effects of PAHs on membrane integrity and permeability to metals, the potential for metal-PAH complexation, the inhibitory nature of metals to the detoxification of PAHs via the cytochrome P450 pathway, the inhibitory nature of PAHs towards the detoxification of metals via metallothionein, and the potentiated production of reactive oxygenated species (ROS) in certain metal (e.g. Cu) and PAH (e.g., phenanthrenequinone) mixtures. Moreover, the mutual inhibition of detoxification suggests the possibility of positive feedback among these mechanisms. The individual toxicities and interactive aspects of contaminant transport, detoxification, and the production of ROS are herein discussed.

Modulation of steroidogenic pathway in rat granulosa cells with subclinical Cd exposure and insulin resistance: an impact on female fertility

Changes in lifestyle lead to insulin resistance (IR) in females ultimately predisposing them towards infertility. In addition, cadmium (Cd), an environmental endocrine disruptor, is reported for detrimental effects on granulosa cells, thus leading to ovarian dysfunction. A combination of these factors, lifestyle and environment, seems to play a role in etiology of idiopathic infertility that accounts for 50% amongst the total infertility cases. To address this issue, we made an attempt to investigate the extent of Cd impact on insulin-resistant (IR) granulosa cells. We exposed adult female Charles Foster rats to dexamethasone and confirmed IR condition by fasting insulin resistance index (FIRI). On treatment of IR rats with Cd, the preliminary studies demonstrated prolonged estrous cyclicity, decrease in serum estradiol concentrations, abnormal histology of ovary, and increased granulosa cell death. Further gene and protein expression studies of steroidogenic acute regulatory (StAR) protein, 17β-hydroxysteroid dehydrogenase (17β-HSD), and cytochrome P450 aromatase (CYP19A1) were performed. Protein expression studies demonstrated significant decrease in treated groups when compared with control. Study revealed that, in spite of the molecular parameters being affected at varied level, overall ovarian physiology is maximally affected in IR and Cd coexposed group, thus mimicking the condition similar to those prevailing in infertile females.